(1) Field of the invention
The present invention generally relates to a liquid jet recording head, and more particularly to a liquid jet recording head from which a liquid drop is jetted by a force generated by a growth of a bubble in a liquid. When an amount of heat energy is supplied to the liquid, the liquid boils and the bubble is generated in the liquid.
(2) Description of related art
In this type of the liquid jet recording head, it is required that responsiveness in a high-speed driving operation be good, that the liquid can be efficiently heated to boiling, and that a durability of the recording head be good. Due to these requirements, material and structure of conventional liquid jet recording head have been improved recently.
In a liquid jet recording head disclosed in Japanese Patent Publication No. 59-34506, an electricity-heat converter constructed of three layers, a bottom layer, a heating resistance layer and a top layer are stacked, to improve the responsiveness and heating property of each electricity-heat converter. In the liquid jet recording head disclosed in Japanese Patent Laid Open Publication No. 60-236758, a thin protection layer is stacked on a heater layer so as to improve the durability.
While the generation of the bubble (main bubble or primary bubble) causing liquid drops to be jetted and the disappearance thereof are repeated sequentially on the heater layer, the following phenomenon, in which a secondary bubble remains on an area of the heater layer, can occur. That is, when an area other than an area on which the main bubble disappears has a temperature greater than a predetermined limit temperature, an elongate secondary bubble extending in a direction in which the liquid flows remains on the area. As a cavitation force of a secondary bubble is greater than that of a main bubble, the heater layer can be damaged by the cavitation force of the secondary bubble. As a result, the durability of the liquid jet recording head deteriorates.
To prevent durability from being affected by the secondary bubble, Japanese Patent Laid Open Publication No. 62-103148 discloses a liquid jet recording head having the following structure. This structure of the liquid jet recording head has been proposed based on a phenomenon in which a center temperature of a heat operation part of the electricity-heat converter is higher than that of a surrounding part thereof in a case where the top and bottom layer of the electricity-heat converter have a constant thickness. That is, the thickness of either the top or bottom layer at the center of the heater operation part is less than that of the layer at the surrounding part thereof so that the center of the heater operation part effectively radiates heat. Thus, the temperature is uniformly distributed on the heater operation part when the heater operation part is activated, and the temperature at a center of the heater operation part is less than the limit temperature when the main bubble disappears due to inactivity of the heater operation part.
In a liquid jet recording head disclosed in Japanese Patent Laid Open Publication No. 59-95155, a conductive member is provided at a center of the electricity-heat converter (a resistance layer) so that no bubble is generated thereon. As a result, the center of the electricity-heat converter is prevented from being damaged by cavitation force. In this case, a ring shaped bubble is grown on a circumference of the electricity-heat converter, and a plurality of small bubbles are distributed, at random, on the heater operation part of the electricity-heat converter.
It is further required for this type of the liquid jet recording head to have a high reproducibility of boiling of the liquid.
In a case where the liquid is repeatedly boiled, when the bubble disappears, small residual bubbles adheres to the surface on the heater operation part of the electricity-heat converter at a position where the bubble has disappeared. Then, when a bubble starts to be generated in a next heat cycle of the electricity-heat converter, the small residual bubbles become a core of the bubble growth. This core is referred to as a bubble core. In a case where a bubble core appears on the surface of the heater operation part, the bubble is prevented from growing normally. That is, high reproducibility of the bubble in the liquid can not be guaranteed. When the reproducibility of the bubble in the liquid decreases, a size of the liquid drop, a jetting speed thereof and the like are varied, so that a quality of the dot images formed on the recording sheet deteriorates.
Japanese Patent Laid Open No. 2-25337 discloses a liquid jet recording head in which the small residual bubbles are prevented from becoming the growing core of the bubble in the next heating cycle of the electricity-heat converter. The residual bubbles are generated on the heater operation part of the electricity-heat converter at the position where the bubble disappears. Thus, when the electricity-heat converter is activated, the temperature of the heater operation part at the position where the bubble disappears is less than that at other positions on the heater operation part. As a result, even if small residual bubbles are generated on the heater operation part at the position where the bubble disappears, the small residual bubbles do not become the growing core of the bubble in the next heating cycle of the electricity-heat converter.
In the liquid jet recording head disclosed in Japanese Patent Laid Open No. 2-25337, the thickness of a heat reserve layer, on which the heating resistance layer is formed, in a part including the position where the bubble disappears is decreased. Due to this structure, the temperature of the part including the position where the bubble disappears can be decreased when the bubble disappears.
However, in the conventional liquid jet recording head, it is difficult to actually form the heat reserve layer in which the thickness thereof varies between the substrate and the heating resistance layer.